Different effects of conventional and biodegradable microplastics on the amelioration process of cadmium-contaminated soil

With the emergence of complex soil pollution problems, the combined contamination of heavy metals and microplastics (MPs) should not be overlooked. Particularly, the safe use of farmland soils deserves more attention. Passivators were commonly used for heavy metal-contaminated soil amelioration. However, the potential impact of MPs on this process is yet to be determined. Herein, the cadmium-contaminated paddy soil was collected to evaluate the effect of MPs on soil properties and bacterial community in soil amelioration. Two types of MPs were investigated, including conventional polyethylene (PE) and biodegradable polylactic acid (PLA). Both MPs decreased the available phosphorus content and bioavailability of cadmium in a similar way, while they changed the soil pH and nitrogen species in a different manner. Additionally, the high-dose PLA treatment induced a considerable decrease in soil pH (from ~5.4 to 3.6), with potential considerable release of carbon substrates and modification of bacterial community. Furthermore, for the ameliorated soil, it has a network structure of less complexity and stabilization, which resulted in greater disparities in the microbial community under different MP treatments. Profiling predicted functions provides insights into the potential correlations among bacterial activities and soil physicochemical properties. The study demonstrated that both PE and PLA could have significant effects on the soil amelioration process and pose a threat to agroecosystems.